Cable logging system

ABSTRACT

A skyline cable logging system in which a skyline carriage runs on a skyline cable ( 106 ) between a yarding hauler ( 101 ) and a remote mobile tailhold ( 113 ) has the remotely controllable mobile tailhold powered and with winch tails which are connected to multiple anchor points ( 110 ). With the skyline tensioned so that the mobile tailhold is aerial the winch tails can be varied to traverse the skyline end between anchor points ( 110 ). The anchor points ( 110 ) can be relocated one at a time to allow the skyline to traverse a large area.

TECHNICAL FIELD

The invention generally relates to a cable logging system for yardingfelled tree stems to a landing area.

More particularly the invention relates to a skyline yarding system inwhich a skyline tailhold is adapted to position itself by controllingthe length of cable tails to anchor points.

BACKGROUND OF THE INVENTION

In timber felling it is normal to place a log yarding machine (“hauler”)with a tower adjacent to a landing area in which logs will be stackedfollowing retrieval after felling at a logging area. The log haulertower supports one or more working wire ropes or cables used inretrieving logs and may also anchor several guy ropes used to preventthe hauler from toppling under load.

The working ropes include one to which logs to be retrieved can besecured, allowing the logs to be dragged or carried from the loggingarea to the landing area. Alternatively a carriage may move along asuspended rope with logs secured to the carriage and another cable maypull the carriage to the landing area.

The working ropes must be anchored to fixed points remotely from thehauler, or must pass through sheaves anchored to fixed points remotefrom the hauler, and typically these points will be topped standingstems or the stumps of felled trees.

This invention relates to a skyline system having a suspended skylinecable, in which a carriage is fully supported on the skyline cableextending from the hauler tower to, normally, a stump to support theskyline cable clear of the ground in operation. The skyline may rundownhill from the hauler allowing the carriage to move down to thelogging area under the influence of gravity (“shotgunning”). Thecarriage may be hauled back to the landing area by the hauler using asecond “mainline” rope secured to the carriage.

This provides an area (the “road”) under and adjacent to the skylinecable which can be reached by choker strops or grapples attached to theskyline carriage. The width of the road is limited by the length of thechoker strops, which are hand placed, or by the grapple suspensionmethod. It is known to provide a further rope from the hauler to thecarriage and deviating from the carriage to an anchor at one side of theroad and back to the hauler. This rope may be part of a circulatingcable (the “haulback”) from the hauler on pulleys anchored on stumps atthe edge of the road allowing the carriage to be pulled towards or awayfrom the hauler or for the carriage and skyline rope to be deviatedsideways to effectively widen the road.

Even so the widening of the road requires the constant shifting of thehaulback anchor points and much opportunity to tangle ropes and endangerpersonnel. It would be desirable to widen the area of the road withoutrequiring excessive movement of anchor points to do it.

The present invention provides a solution to this and other problemswhich offers advantages over the prior art or which will at leastprovide the public with a useful choice.

All references, including any patents or patent applications cited inthis specification are hereby incorporated by reference. No admission ismade that any reference constitutes prior art. The discussion of thereferences states what their authors assert, and the applicants reservethe right to challenge the accuracy and pertinency of the citeddocuments. It will be clearly understood that, although a number ofprior art publications are referred to herein; this reference does notconstitute an admission that any of these documents form part of thecommon general knowledge in the art, in New Zealand or in any othercountry.

BRIEF SUMMARY OF THE INVENTION

In one exemplification the invention consists in a mobile tailhold for askyline logging system, the mobile tailhold having at least two mobiletailhold powered winchable cable tails, the cable tails being winchableby at least one mobile tailhold mounted winch, the cable tails eachbeing attachable to an anchoring point such that the mobile tailhold canbe positioned relative to the anchor points by winching the cable tailswith the at least one mobile tailhold mounted winch.

Preferably the mobile tailhold is attached to a skyline cable and islifted above the ground in use.

Preferably the mobile tailhold is fixedly attached to a skyline cable asa tailhold.

Preferably the mobile tailhold is movably attached to a skyline cable.

Preferably the mobile tailhold is movable aerially laterally of theskyline cable by shortening one of the mobile tailhold powered winchablecable tails when attached to an anchor point and lengthening another ofthe mobile tailhold powered winchable cable tails when attached to ananchor point.

Preferably the at least one mobile tailhold mounted winch is a dual drumcapstan winch in which the capstan drums counter-rotate and a cable iswrapped in opposing directions around each of the dual drums to providethe winchable cable tails.

Preferably the drums of the dual drum capstan are geared tocounter-rotate synchronously.

Preferably the winchable cable tails are winched by separate mobiletailhold powered winches.

Preferably the winchable cable tails exit the tailhold through fairleadswhich fairleads monitor the cable tail exit angle.

In another exemplification the invention consists in a skyline loggingsystem having at least a skyline cable supported between a hauler and anaerial mobile tailhold, the mobile tailhold being anchorable to at leasttwo separate tail anchor points by cable tails, the mobile tailholdhaving at least one mobile tailhold powered winch adapted to separatelypay out or pull in the cable tails, the mobile tailhold being movableaerially from adjacent one anchor point to adjacent another anchor pointby paying out one cable tail and pulling in another cable tail.

Preferably the mobile tailhold has two mobile tailhold powered winchesseparately controlling the tension in cable tails to two tail anchorpoints.

Preferably the mobile tailhold has a single anchoring cable with a cabletail extending to each of two different tail anchor points and has amobile tailhold powered capstan around which an intermediate portion ofthe cable is wrapped.

Preferably the tailhold has a capstan having two capstan drums and thecable wraps both drums at least once.

Preferably the two capstan drums of the tailhold counter-rotate and thecable wraps in opposite directions around each drum.

Preferably the two capstan drums are geared to counter-rotatesynchronously.

Preferably the mobile tailhold is supportable from the skyline cable andis adapted to travel along the skyline cable.

-   -   In a further exemplification the invention consists in a lateral        deflection jack for a cable logging system, the jack having a        frame capable of being attached to an anchor point, at least one        pivoted cable receiving shoe pivoted from the frame, the        pivotable cable receiving shoe having spaced upper and lower        plates, the upper plate having a substantially flat upper        surface, the space between the upper and lower plates defining a        cable receiving recess, the upper plate being over-rideable by        at least one supporting sheave of a carriage, the carriage        running on a cable received in the space between the upper and        lower plates.

These and other features of as well as advantages which characterise thepresent invention will be apparent upon reading of the followingdetailed description and review of the associated drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a hauler and skyline.

FIG. 2 is a perspective view of the hauler end of the skyline of FIG. 1.

FIG. 3 is a perspective view of the carriage 108 of FIG. 1 from oneside.

FIG. 4 is a perspective view of the carriage 108 of FIG. 1 from theother side.

FIG. 5 is a perspective view of a lateral deflection jack used in theskyline system.

FIG. 6 and FIG. 7 show differing perspective views of a lateraldeflection jack.

FIG. 8 shows the skyline entraining shoes of a lateral deflection jack.

FIG. 9 shows a view of a carriage passing over a lateral deflection jack

FIG. 10 shows the tail of a skyline secured to a mobile tailhold.

FIG. 11 shows one version of a mobile tailhold.

FIG. 12 shows a side persective view of a second form of mobiletailhold.

FIG. 13 shows a top perspective view of the second form of mobiletailhold.

FIG. 14 shows a perspective view of a third form of mobile tailhold.

FIG. 15 shows a perspective view of a fourth form of mobile tailhold.

DESCRIPTION OF THE INVENTION

FIG. 1 shows a diagram of a skyline logging system, with FIG. 2 showinga more detailed diagram of the skyline hauler positioning in typicalterrain. A hauler 101 is tracked to allow it to access difficult loggingsites and has a raisable tower 102 carrying at the top shackles to whichanchor cables 103 may be attached for securing to ground anchors,typically tree stumps 104. These prevent the tension of the skylinecable 106 and load from tipping the hauler over. The top of the toweralso carries pulleys 105 to allow reeling in and out from one or morewinches in the hauler the skyline cable and other working ropes. Ahauler may, for instance, have winches for the skyline, the mainline,the haulback feed and the haulback return. Preferably the hauler isabove the logging site as this allows shotgunning the carriage down theskyline to pick up a load and does not require careful control of heavydownhill loads.

The hauler 101 may have a drivers cab 111 or may be remotely controlledand may have a grappler 112 to assist in stacking timber when carried tothe hauler on the skyline cable 106. The operator may control the loadson the skyline cable and communicates with the loggers in the road byradio or sound signals on a horn.

Sometimes control passes to an in-field operative for the grappling andchoking phase then reverts to the operator of the hauler after the loadhas automatically returned to a spot just before the hauler. In thiscase an operator in perhaps a separate unloading excavator may take overcontrol.

The hauler 101 can have the tower 102 and drivers cab 111 on a turntableplatform, allowing rotation of the entire rig in place on the tracks orwheels, but this is restricted if the tower 102 is guyed since itbecomes impossible to easily rotate the tower. It is proposed to providea central rotatable turntable platform mounting the tower 102 and anouter rotatable platform mounting the drivers cab 111 and grapple. Inthis way each may be independently rotated allowing the driver thefreedom to place stems anywhere around the hauler.

The skyline cable has a carriage 108 which rides on the cable and thecarriage may have a controllable grapple 109 (FIG. 2) to hold and bunchstems or it may have choker strops which may be attached to logs toallow them to be dragged back to the hauler. To allow dragging thecarriage 108 may be self-powered by a controllable inbuilt enginedriving the sheaves which ride on the skyline 106 or there may be amainline 107 with which the hauler driver drags the carriage to theloader.

The skyline 106 is normally attached at the tail end to a tree stump orto a standing stem, but FIG. 1 shows a variation in which a loop cableattached to stumps 110 passes through a tailhold capstan at a suspendedskyline tailhold anchor 113, better described with reference to FIG. 10.

FIGS. 3 and 4 show carriage 108 suspended on skyline cable 106 bysheaves 114. The sheaves have a central groove to capture skyline 106.Sheaves 114 have outer flanges which define the edges of a cylindricalsurface on both sides of the central groove. An engine 116 within thecarriage can supply hydraulic power to wheels 115 which can engage theskyline cable 106 from below, allowing the engine 116 to power thecarriage along the skyline cable or to brake the carriage againstmovement along the skyline cable 106. The sheaves 114 and wheels 115 maybe attached to uprights 122 which are pivoted to allow pivoting of thesheaves and wheels about a vertical axis.

Wheels 115 are actuable to and from engagement with skyline cable 106and may be of rubber engaging under considerable pressure against thecable 106 and sheaves 114, thus generating considerable deformationfriction. Because some movement of the wheel surface is still requiredfor coping with jacks and other irregularities a pneumatic tyre may beused as a wheel 115. In tests a single driven tyre at 90 psi provided700 Kg of tractive effort in any conditions. Preferably the tyre is ahigh pressure tyre such as an aircraft tyre from a high wheel loadingaircraft type. If more traction is required then more than a singlewheel 115 and sheave 114 on each end of the carriage may be provided.This allows a powered carriage to move appreciable loads while stillhaving a skyline cable which does not require a convoluted path throughthe carriage to achieve the required driving friction level. This inturn allows easy passage past a jack.

A mainline cable 107 may be provided, normally passing through thecarriage to allow the end to be used for attaching stems, but with aswaged end 119 to bind the mainline cable 107 against a stop if thecarriage 109 is to be hauled by the hauler.

The engine 116 may also supply power to rotate grappler 109 and toseparately control bunching arms 117 and grappler arms 118. Control ofall the carriage functions may be by radio control from either thehauler operator or by a controller in the road with assistance from acamera either on the carriage or attached to a separate small carriageon the skyline. The camera carriage too may be self-powered, typicallyby a battery supply.

FIG. 5 shows a variation of the skyline system in which the skyline isdiverted sideways around a lateral deflection jack to widen the roadaccessible. Upright jacks are in common use in skyline systems to raisethe skyline cable clear of the terrain. Such jacks normally consist of asheave at tip of a J-shaped support. The upper shank of the J issupported by a standing trunk and the sheave at the tip of the Jsupports the skyline. A carriage with sheaves open on one side at thetop and a gap below allows the carriage to pass over the jack, howeverthe amount of lateral movement of a skyline provided by an upright jackis severely limited because the sheave support will contact the carriagebut such jacks are usable for small deflection angles.

FIG. 5 shows a skyline cable 106 and a lateral deflection jack 125pulled towards standing stem 127 by cable 126. The jack may be depressedwith respect to the skyline 106 or it may also raise skyline 126 but itsprincipal use is to deflect the skyline cable 106 sideways.

FIGS. 6 and 7 show an example of such a jack 125 where frame 128includes a motor 131 which may be remotely controlled to operate winchdrum 132. The winch drum winds a rope (not shown) which passes throughrollers 133 and is secured to an anchor such as stem 127 of FIG. 5. Thetension on the winch rope controls the amount of lateral deflection ofthe skyline cable 106. The skyline cable passes through shoes 130pivotally supported on frame arms 129. The shoes may incorporate sheavesto allow easy movement of the skyline cable through them if necessary.

The deflection of the skyline cable may be increased temporarily toallow grappling a stem, but returned to a less deviated path beforemoving the stem far in order to remain within safe working load of theskyline cable 106.

FIG. 8 shows shoes 130 consisting of top plate 150, bottom plate 151 andspacing and wear plates 152. A sheave 154 may be encased within the wearplates to allow the skyline cable to be passed across the shoe withminimal friction. The shoe is pivotally affixed to a frame arm 129 atprojection 155 by a flush pin 156.

FIG. 9 shows a carriage 108 in transit across a lateral deflection jack125. Shoes 130 are of low enough profile that they have passed betweensheave 114 and wheel 115 and are sized to fit between the flanges ofwheels 115 and sheaves 114 and engage the cylindrical surface of thesheave 114. This ensures that the carriage sheaves cannot derail intheir passage.

The lateral deflection jack 125 is sized to just clear the carriagecontainer. The result is that if the jack tail anchor 126 is slacked offand removed from its anchor point when a carriage is halted in transitas in FIG. 8 the jack 125 will bind against carriage 108. The skylinewill revert to its normal route and the carriage can transport thelateral deflection jack 125 to a new location for attachment to a newanchor. Tightening the jack winch will then tension the skylinesideways, lifting the lateral deflection jack clear of the carriage andallowing the carriage to transit the jack 125.

FIG. 10 shows the tail of the skyline 106. A mobile tailhold 113 isattached to tailhold cables 135, 140 anchored on each side at 110. Themobile tailhold is shown in FIG. 10 and consists of a frame with sheaves136 allowing it to travel on skyline cable 106 and includes a lock tolock it in place on the skyline cable. Typically the mobile tailholdwith a skyline extended to it is placed near an anchor 110 and a tailrope 140 is extended to the anchor. The tail rope can then be tensionedto pull the mobile tailhold towards the anchor so that eventually theskyline can be fully tensioned. The skyline may be directly connected tothe anchor 110 or the mobile tailhold may act a mobile anchor with theopportunity to connect to a second anchor via cable 135. Capstan 137 onthe mobile tailhold, capable of being driven by motor 138 may be rotatedto advance the mobile tailhold between the two anchors 110. In this waythe width of the road may be extended at the tail end of the skylinewithout providing many separate tail anchors. The tailhold may beconsidered mobile if it is translatable in position while in operation.

When a road is worked out for the whole width of the available movementof the mobile tailhold 113 it is grounded near an anchor 110 by relaxingthe skyline, the tailhold cable removed from the other anchor 110 andextended past the remaining anchor to a new anchor. The skyline is againtensioned to lift the mobile tailhold providing a new road width forprocessing with very little manual labour.

Other combinations of ropes may be used to position the mobile tailhold,for instance given a single fixed anchor for the skyline cable 106 themobile tailhold may be run down the skyline to the only tailhold,another laterally placed tailhold anchor established with a tailholdcable from the mobile tailhold and a wider road provided by translatingthe mobile tailhold laterally. When the available roads are allprocessed the skyline may revert to a single anchor, the mobile tailholdcan be pulled back to the hauler with the mainline, and the skyline thenbe retrieved.

The mobile tailhold itself may have varying combinations of ropehandling gear to allow enhanced operations, for instance the tail holdshown in FIG. 11 has a single capstan, a single winch, and skylinesupports but variations may include twin winches or a double capstan.FIGS. 12 and 13 show a version with a frame 145 which has two winches141, 142 running through horizontal sheaves 143, 144 to laterally spacedanchors. Such variations allow the tailhold to be moved to differentpositions more readily and may also allow the mobile tailhold to performsmall yarding operations to move stems to within reach of the skyline.

FIG. 14 shows a mobile tailhold variation in which a tub frame 160 has apowered hydraulic unit 161 which may drive two counter-rotating winchdrums 162, 163 which are wrapped by a single cable 164 with two ends 164and 165. The winch drums are hydraulically driven and are synchronisedby interengaging gears 167, 168. The multiple wraps of cable 164 aroundthe two drums provides good purchase on the cable to give a goodwinching ability in either direction. Brakes 168, 169 may be applied tothe cable to hold it in one position.

The cable exits through tiltable sheaves 170, 171 through fairleads 174,175 so that the sheaves will cope with comparatively large horizontaland vertical deflection of the cable ends 164, 165. Fairleads 174, 175may have deflection sensors so that if the divergence of a cable end istoo high an alarm is tripped and the winch stopped.

In use a skyline cable may be fixed to eye 178. Sheaves 176 and 177 maybe provided to allow the mobile tailhold to be transported on theskyline when that is secured to a fixed anchor point for initiallocation or retrieval.

FIG. 15 shows a variation of a two winch tailhold in which a tub frame180 has a powered hydraulic unit 181 and two winch drums 182, 185 whichare driven respectively by hydraulic motors 183 and 186 via chain drives184, 187. Pawl stops 188, 189 are provided to brake the winch drums.Cables 190, 191 are wound on their respective winch drums 182, 185. Thecables 190, 191 exit the mobile tailhold via sheaves 194, 195 which areflexibly mounted by chain links 196.

Eye 199 is attached to the skyline cable 200 and additional outriggerarms with eyes 201, 202 may be mounted on the tub 180 to provideadditional securing points for other cables.

In deploying such a mobile tailhold a skyline is deployed to a fixedanchor point from a hauler, the skyline is relaxed and a mobile tailholdplaced on the skyline at the hauler. The skyline is tensioned and themobile tailhold mainlined out to the fixed anchor point where theskyline is again relaxed, connected to the skyline eye on the mobiletailhold, and a tail on the tail hold paid out and connected to thefixed anchor point.

The skyline is again tensioned, lifting the mobile tailhold from theground to an aerial position and allowing a second tail from the tailhold to be paid out and attached to a laterally located anchor point.The mobile tailhold can now be translated aerially laterally between thetwo fixed anchor points by paying out one tail and pulling in the otherthus moving the skyline end laterally. When the tailhold needs to bemoved further laterally it can be grounded at one extent of its travel,the nearest of the anchor point tails removed from the anchor and placedlaterally further away while the other is retrieved from the otheranchor point and placed on the vacated anchor point. The skyline canthen be retensioned to lift the mobile tail hold again.

Control of the functions of the mobile tailholds may be shared betweenthe hauler operator and a controller in the road.

The hauler shown is a track based hauler with a separate controllablegrapple, but haulers with only a tower, or on wheeled self-poweredplatforms or trailers may be used.

Variations

While the invention is described in relation to a skyline logging systemwith only a skyline and a mainline it is equally applicable to a systemwith skyline, mainline and haulbacks.

The lateral deflection jack is described as using flanged cylindricalsheaves with a cable groove but other configurations of sheave and jackplates may be used, the requirement being that the jack will retain theskyline cable so long as the jack tail is under tension, and that thecarriage on the skyline can override the jack.

The carriage, lateral deflection jack and mobile tailhold are alldescribed as having engines to drive wheels, winches or capstans. Theseengines may be small diesel/hydraulic engines, battery drivenelectric/hydraulic motors or they may be various combinations ofhaulback or mainline powered gearing. Any method of providing therequired motive power is satisfactory. The mobile tailholds may be usedto vary the position of a lateral deflection jack by shifting it alongthe skyline path. Since loads at the lateral deflection jack are not asextreme as those at a tailhold a lighter version of the tailhold may beused. To further reduce the weight of a light tailhold or a lateraldeflection jack the anchor ropes or cables may be synthetic, forinstance of Kevlar.

Control of the mobile tailhold is preferably by radio for functions suchas winch control or winch braking, with detection of parameters such astail cable overload.

Because the skyline carriage may well be operating out of sight of thehauler operator the control system will typically be based on secureradio and video links with the transmitters for these forming part ofthe structure of equipment such as cameras, jacks and carriages. Aground operator in the skyline road may be assisted by video glasses andcontrol gloves for the equipment linked in to this system.

While the system is described as delivering stems to a yarder it mayequally be used to deliver stems from a yarder to a remote loadingpoint.

A person skilled in the art will realise that other mechanisms mayprovide the required operations and may be substituted as required.

It is to be understood that even though numerous characteristics andadvantages of the various embodiments of the present invention have beenset forth in the foregoing description, together with details of thestructure and functioning of various embodiments of the invention, thisdisclosure is illustrative only, and changes may be made in detail solong as the functioning of the invention is not adversely affected. Forexample the particular elements of the controllers for the devices mayvary dependent on the particular application for which it is usedwithout variation in the spirit and scope of the present invention.

In addition, although the preferred embodiments described herein aredirected to a tree felling head, it will be appreciated by those skilledin the art that variations and modifications are possible within thescope of the appended claims.

1. A mobile tailhold for a skyline logging system, the mobile tailholdhaving at least two mobile tailhold powered winchable cable tails, thecable tails being winchable by at least one mobile tailhold mountedwinch, the cable tails each being attachable to an anchoring point suchthat the mobile tailhold can be positioned relative to the anchor pointsby winching the cable tails with the at least one mobile tailholdmounted winch.
 2. A mobile tailhold for a skyline logging system asclaimed in claim 1 wherein the mobile tailhold is attached to a skylinecable and is lifted above the ground in use.
 3. A mobile tailhold for askyline logging system as claimed in claim 2 wherein the mobile tailholdis fixedly attached to a skyline cable as a tailhold.
 4. A mobiletailhold for a skyline logging system as claimed in claim 2 wherein themobile tailhold is movably attached to a skyline cable.
 5. A mobiletailhold for a skyline logging system as claimed in claim 2 wherein themobile tailhold is movable aerially laterally of the skyline cable byshortening one of the mobile tailhold powered winchable cable tails whenattached to an anchor point and lengthening another of the mobiletailhold powered winchable cable tails when attached to an anchor point.6. A mobile tailhold for a skyline logging system as claimed in claim 1wherein the at least one mobile tailhold mounted winch is a dual drumcapstan winch in which the capstan drums counter-rotate and a cable iswrapped in opposing directions around each of the dual drums to providethe winchable cable tails.
 7. A mobile tailhold for a skyline loggingsystem as claimed in claim 5 wherein the drums of the dual drum capstanare geared to counter-rotate synchronously.
 8. A mobile tailhold for askyline logging system as claimed in claim 1 wherein the winchable cabletails are winched by separate mobile tailhold powered winches.
 9. Amobile tailhold for a skyline logging system as claimed in claim 1wherein the winchable cable tails exit the tailhold through fairleadswhich fairleads monitor the cable tail exit angle.
 10. A skyline loggingsystem having at least a skyline cable supported between a hauler and anaerial mobile tailhold, the mobile tailhold being anchorable to at leasttwo separate tail anchor points by cable tails, the mobile tailholdhaving at least one mobile tailhold powered winch adapted to separatelypay out or pull in the cable tails, the mobile tailhold being movableaerially from adjacent one anchor point to adjacent another anchor pointby paying out one cable tail and pulling in another cable tail.
 11. Askyline logging system as claimed in claim 10 wherein the mobiletailhold has two mobile tailhold powered winches separately controllingthe tension in cable tails to two tail anchor points.
 12. A skylinelogging system as claimed in claim 10 wherein the mobile tailhold has asingle anchoring cable with a cable tail extending to each of twodifferent tail anchor points and has a mobile tailhold powered capstanaround which an intermediate portion of the cable is wrapped.
 13. Askyline logging system as claimed in claim 10 wherein the tailhold has acapstan having two capstan drums and the cable wraps both drums at leastonce.
 14. A skyline logging system as claimed in claim 13 wherein thetwo capstan drums of the tailhold counter-rotate, are geared tocounter-rotate synchronously and the cable wraps in opposite directionsaround each drum.
 15. A skyline logging system as claimed in claim 10wherein the mobile tailhold is supportable from the skyline cable and isadapted to travel along the skyline cable.
 16. A lateral deflection jackfor a cable logging system, the jack having a flame capable of beingattached to an anchor point, at least one pivoted cable receiving shoepivoted from the frame, the pivotable cable receiving shoe having spacedupper and lower plates, the upper plate having a substantially flatupper surface, the space between the upper and lower plates defining acable receiving recess, the upper plate being over-rideable by at leastone supporting sheave of a carriage, the carriage running on a cablereceived in the space between the upper and lower plates.